As a frequenter of the Fringe (not a performer though), I can tell you the following:
- Leaflets/ Flyering.
You stand in the street and hand them out. It's a self promotion exercise. Some people choose to do busking slots on the Royal Mile to promote their shows too. there are loads of poster boards around the town which I believe require payment in order to allow you to put up your own. You can also pay to get listed in the Fringe guide. It is pricey! See link below.
- What are the audience's like, mood, size etc.
It depends if you are planning to charge, time and location (mainly the popularity of the venue and how close to the centre it is).
If you are planning on doing it free (recommended for a Fringe starter to get better known), you will get bigger crowds who are not too bothered about the quality. Most who do free shows have a well practised, friendly spiel at the end about how they do it for free and how a contribution, in the form of pound coins, for their work would be very welcome. Often they throw in a joke to make it easier to swallow.
If you are expecting to sell tickets, you are going to have to invest in serious promotion and your name needs to proceed you, since a lot of people buy their festival tickets in advance when the Fringe guide comes out in June.
There are a couple of Free Fringe organisations you can probably get involved with. They put on shows in various functions rooms in bars and clubs. There is no problem with you asking for contributions at the end and they already put on some magicians.
- How long should the show be.
Most Fringe venues timetables are split up into hour long slots.
I have been eyeing up doing something at the Fringe for a while... I keep chickening out.
Good for you if you do it!
More information:
http://www.edfringe.com/participants